I've put together two graphs covering the top 5 SOpedias (Jon Skeet, Marc Gravell, tvansfosson, S.Lott and JarPar) plus myself and Jeff Atwood for kicks. The two graphs look at Day of Week and Time of Day.

My conclusion as for the best time to ask a question? Assuming the importance of the Fast Gun in the West phenomena, then...

On a Tuesday, Wednesday or Thursday (in that order)

If you want Jon Skeet to answer it, then most defiantly a Tuesday

Between 1300 and 2100 GMT

The best possible chance of getting Jon Skeet or Marc Gravell (#1 and #2 SOpedians) to answer your question (and not one of the other tens of thougsands of users), then sometime between 0700 and 1300 GMT on a Tuesday

From the July 2009 data dump, top 5 determined by today's standing in reputation points

@akf: It seems that Kyle and I both have meetings on Wednesdays. Conspiracy? :P
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Stu ThompsonJul 27 '09 at 7:10

@Stu: Thanks - I hope it hasn't cluttered the graph too much. I find it interesting how my daily activity is almost the reverse of the rest of SO - I'm most active on the weekends and least active during the week.
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Kyle CroninJul 27 '09 at 17:03

@Kyle: I had actually removed folks from the graphs as I was developing them because they were too cluttered. Joel Coehoorn stood out in earlier statistics as someone who bucked the trend, like you. He just does not spend much time on SO on the weekends (1.5% on Saturdays, 2.4% on Sundays)...must have a life or something similar ;) All this has inspired me to do similar themed graphs...more later....
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Stu ThompsonJul 27 '09 at 17:23

Only the top 5? Bah! I'm in New Zealand, so it might be interesting to add me for a non-western-hemisphere data point.
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Greg HewgillJul 31 '09 at 4:23

It may be the case that the time you post does not significantly affect the total number of views it gets. Think about the front page exposure, for example: on a particularly busy moment your question spends less time on the front page than it would at a quieter time, so I'm not sure posting at a active moment helps that much.

Now, to maximise the amount of answers early on (which leads to more exposure on front page, and, in many cases, to very high-quality answers eventually, as people compete honing their answers), follow these guidelines: ;-)

the topic shouldn't be anything obscure (preferably about C# or Java)

the question should be pretty easy (e.g. "Why isn't there a get(index) method in a Set")

the question might be ever so slightly provocative or controversial

(I'm not too serious about that, but it is a fact that more difficult questions, or ones concerning a little less-trodden topics, are often left without that many views, or any good answers.)